2. 职称英语
  3. This passage is excerpted from material published in 1997. Is there a massiv

This passage is excerpted from material published in 1997. Is there a massiv

游客2024-01-12  69
问题 This passage is excerpted from material published in 1997.
    Is there a massive black hole at the center of our galaxy, the Milky Way? The evidence is inconclusive. Just as the Sun’s mass can be determined, given knowledge of other variables, by the velocity at which its planets orbit, the mass at the center of the Milky Way can be revealed by the velocities of stars and gas orbiting the galactic center. This dynamical evidence, based on recently confirmed assumptions about the stars’ velocities, argues for an extremely compact object with a mass two to three million times the mass of our Sun. Although according to current theory this makes the mass at the center of the galaxy too dense to be anything but a black hole, the relative lack of energy radiating from the galactic center presents a serious problem. A black hole’s gravity attracts surrounding matter, which swirls around the black hole, emitting some energy as it is engulfed. Scientists believe that the amount of energy that escapes the black hole should be about 10 percent of the matter’s rest energy (the energy equivalent of its mass according to the equation E=mc2). But when the energy coming from the galactic center is compared to widely held predictions based on how much matter should be falling into a theoretical central black hole, there is a discrepancy by a factor of a few thousand.  [br] According to the passage, the dynamical evidence referred to in lines 9-10 supports which of the following?
选项 A、Recent assumptions about the velocities of stars
B、Widely held predictions about the amount of matter a black hole will engulf
C、The existence of an extremely dense object at the center of the Milky Way
D、The contention that too much energy is coming from the mass at the Milky Way’s galactic center for that mass to be a black hole
E、The conclusion that a compact object of two to three million times the mass of our Sun is too dense to be anything but a black hole
答案 C
解析 What does the passage claim the dynamical evidence mentioned supports? The passage states that the dynamical evidence argues for an extremely compact object with a mass two to three million times the mass of our Sun at the center of the Milky Way. An extremely compact object with such a mass would, of course, be tremendously dense.
A     The passage in no way suggests that the dynamical evidence mentioned supports assumptions about the velocities of stars Rather, it states that the assumptions about the velocities of the stars have been "recently confirmed" and that the dynamical evidence is actually based on these assumptions. If the dynamical evidence is a product or these assumptions, then it cannot be used to support them.
B     The passage suggests that the dynamic a evidence is consistent with the existence in the Milky Way of an extremely dense object that is likely a black hole. However, the evidence in no way suggests that reliable predictions can be made about how much matter such a hypothetical black hole would engulf.
C     Correct. As indicated above, this refers to the extremely compact object of immense mass; this object would of course be "extremely dense."
D     This choice presents a suggestion opposite to the information in the passage. The passage suggests that the object at the center of the Milky Way is in fact radiating too little to be easily identifiable as a black hole.
E     The passage acknowledges that the density of the mass at the center of the Milky Way is consistent with the existence of a black hole there. However, the passage further suggests that an unexpectedly small quantity of energy radiating outward from the center of the Milky Way calls this into question.
The correct answer is C.
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